Interleaving bisimilarity was proved undecidable in [1]}, with a proof based on the comparison of two sequential P/T nets,
where a P/T net is sequential if it does not offer any concurrent behavior. Hence, interleaving bisimulation equivalence is
undecidable even for the subclass of sequential finite P/T nets. Esparza observed in [2]} that all the non-interleaving
bisimulation-based equivalences –  in the spectrum ranging from interleaving bisimilarity to fully-concurrent bisimilarity [3]}
– 
collapse to interleaving bisimilarity over sequential P/T nets. Hence, the proof in [1]} applies to all these
non-interleaving bisimulation equivalences as well.
